<!DOCTYPE html>
<style>
    .container {
        font: 10px/1 Ahem;
        color: green;
    }
    .left {
        float: left;
        height: 10px;
        width: 50px;
        background-color: red;
        shape-outside: inset(0 100% 0 0);
    }
</style>
<body>
    You should see a green rectangle. You shouldn't see any red.
    <div class="container">
        <div class="left"></div>
        XXXXX
    </div>
</body>
